1. Field of the Invention
The present invention relates to a differential flat spiral delay line structure, and more particularly to a differential flat spiral delay line structure with grounding guard traces and strong coupling line parts.
2. Description of the Prior Art
Signal synchronizing is always a concern when it comes to the high speed digital signal. Usually the requirement of synchronizing signals is met by increasing the delay time with a delay line. To be more specific, for high speed signal or signal over shorter transmission circuit, a delay line structure is usually used in order to delay the transmission time.
Due to limited space in the substrate of an electronic device, the delay line is usually bent in order save the occupying space. There are various delay lines, among which a differential flat spiral delay line is very common. The following describes a differential flat spiral delay line structure of the prior art.
Referring to FIG. 1, FIG. 1 illustrates a differential flat spiral delay line structure in the prior art. A differential flat spiral delay line structure 1 is fabricated on a substrate 100, and includes two spiral delay lines 11 and 12.
To those skilled persons in the art, the prior art differential flat spiral delay line structure 1 encounters two serious problems. Firstly, crosstalk noise disturbance is generally resulted between an adjacent pair of the straight sections in the spiral delay lines, thereby affecting a waveform of a received signal, which leads to misinterpretation on a voltage level of a digital received signal. Secondly, due to unequal lengths at the outer and inner bent sections of the spiral delay lines 11 and 12, signal synchronizing for transmission the signals at the same rate is hard to achieve. Although grounding guard traces are applied to reduce the crosstalk noise disturbance, the result is still not ideal.